During driving operation, the tractive vehicle and the trailer vehicle are constantly joined together mechanically by a coupling device. By a tractive vehicle and a trailer vehicle is meant a tractor-trailer combination, which usually consists of an articulated tractor as the tractive vehicle and an articulated trailer as the trailer vehicle. The two vehicles in this case are detachably coupled together by a coupling mechanism comprising a fifth wheel and a king pin. But the invention can also be implemented on an articulated vehicle consisting of a motor vehicle as the tractive vehicle and a trailer as the trailer vehicle. Such vehicles are usually joined together by means of a coupling mechanism comprising a bolt coupling and a tow bar secured therein. Furthermore, it is also possible in the case of multiple trailer vehicles for the tractive vehicle to comprise a front articulated trailer or plain trailer arranged closer to the tractive vehicle and for the trailer vehicle to comprise a rear articulated trailer or plain trailer further away from the articulated tractor or motor vehicle.
Between the tractive vehicle and the trailer vehicle in the coupled state there is a gap, which produces considerable turbulence of the passing air during travel and thus causes a relatively high fuel consumption. However, a minimum gap width is needed, since a relative movement between tractive vehicle and trailer vehicle occurs especially when negotiating curves and without it there is the danger of the front edge of the trailer vehicle on the inside of the curve colliding with the tractive vehicle in the case of a sharp curve. Also during abrupt braking parts of the trailer vehicle can strike against the tractive vehicle on account of shifting of the payload.
In the past, therefore, efforts were already made to cover the gap between tractive vehicle and trailer vehicle, for example with air guiding elements. For example, from U.S. Pat. No. 3,711,146 there is known an air guiding apron engaging with the rear wall of the driver's cabin, comprising several telescoping segments in the lengthwise axis of the vehicle. Before driving away, the segments are pulled out and the width of the air guiding apron is adjusted to the width of the actual gap so that the gap is largely covered. The segment of the air guiding apron adjoining a trailer should be made of rubber or another elastic material and allow for the impact of parts of the trailer when driving along larger curve radii. For narrow curve radii or a changing of trailers, the air guiding apron can be pushed back manually or by means of servo cylinders in the direction of the driver's cabin. The major drawback to this known air guiding apron is its adjustment before driving away and the resulting unavoidable impact of the trailer against the air guiding apron. This always causes damage to the air guiding apron or the trailer.
A generic prior art is U.S. Pat. No. 3,834,752. The bridging of the gap between tractive vehicle and trailer vehicle in this case is realized by means of an inflatable air bag, which is arranged on the front end of the trailer vehicle and after the coupling on of the tractive vehicle it is detachably secured to the rear wall of the driver's cabin. The otherwise closed air bag is inflated via a compressed air line of the tractive vehicle and thereby stabilized. The compressed air supply of the air bag should come in particular via the compressor of the vehicle brake system. It has proven to be a drawback that the tractive vehicle needs to be outfitted with a substantial compressor power in order to fill the volume of the air bag, several cubic meters in size, in addition to the braking system. This problem is further aggravated when the air bag loses tightness due to damage and therefore the compressor is no longer able to fill the pressure accumulator of the brake system. In some cases, this may lead to loss of the brake system, so that the articulated vehicle is disabled from driving.